The overall goal of this project is to investigate physiological mechanisms regulating airway reactivity under two conditions: (1) during immunological stimulation (antigen challenge) and (2) during non-immunological stimulation (endogenous release of substance P). Based on our previously reported observations and additional preliminary data, several hypotheses may be postulated; the specific aims of this project are to test these hypotheses. This proposal is designed to carry out the aims as follows. (1) During antigen challenge-induced airway spasm, effects of the nonadrenergic noncholinergic inhibitory system will be examined using free oxyhemoglobin to suppress the inhibitory system. In addition, we plan to explore further the relationship between this inhibitory system and guanosine 3',5'-monophosphate (cyclic GMP). Cyclic GMP will be determined during activation of the inhibitory system. (2) The effects of endogenous substance P on airways and axon reflex in the lungs will be examined. It is postulated that endogenous substance P can induce constrictions of both central (large) and peripheral (small) airways and is an important neurotransmitter of the axon reflex. Both air and helium maximum expiratory flow-volume curves will be generated and used to locate physiologically the sites of airway constriction. Ganglionic and sodium channel blocking agents as well as substance P antagonists will be employed to investigate the relationship between substance P and the axon reflex. (3) We found previously that exsanguination enhances postmortem bronchoconstriction. Similarly, other investigators showed that ligation of the left pulmonary artery induces focal atelectasis in the left lung. We have hypothesized that increased oxygen radicals during ischemia enhance the release of endogenous substance P, and that exsanguination decreases the enzyme to degrade substance P and/or decreases carrier macromolecules to bind substance P. To test these hypotheses, substances P will be measured by radioimmunoassay following exsanguination, incubation with lung lavage or adsorption with charcoal. (4) We postulated that endogenous release of substance P and/or the sensitivity of airway smooth muscle to substance P are age- dependent. Testing of this hypothesis can help us to learn why substance P-induced bronchoconstriction diminishes with maturation.